Morphine and structural analogs of morphine (the “morphine alkaloids”) such as codeine, hydrocodone, hydromorphone, naloxone, naltrexone, oxycodone and oxymorphone are used in analgesic prescription drugs. Other morphine analogs, e.g., thebaine, are useful starting materials for preparing analgesic morphine alkaloids. However, thebaine is only a minor component of the morphine alkaloids found in the seeds of poppy plants, and synthetic methods for preparing thebaine are relatively costly (see U.S. Pat. No. 6,262,266 B1 to Chiu et al.).
Codeinone dienol acetate, which is the 3-O-methyl derivative of morphinone dienol acetate, is a morphine alkaloid useful for preparing analgesic and antagonistic morphine alkaloids such as naloxone, naltrexone and oxycodone (see, e.g., U.S. Pat. No. 6,013,796 to Huang et al.). Codeinone dienol acetate can be prepared by oxidation of codeine to codeinone followed by acylation (see, e.g., U.S. Pat. No. 6,013,796 to Huang et al.).
Other 3-O-protected-morphinone dienol carboxylates are known and are generally prepared by oxidation of the corresponding 3-O-protected-morphine followed by acylation. A number of these 3-O-protected-morphinone dienol carboxylates have been used to prepare other useful morphine alkaloids.
The following paragraphs relate to known methods for making 3-O-protected morphinones by oxidation of the corresponding 3-O-protected morphines.
Codeine is 3-O-methylmorphine and codeinone is 3-O-methylmorphinone.
U.S. Pat. No. 2,654,756 to Homeyer et al. describes the reaction of codeine with aluminum tri(tert-butoxide) and methoxycyclohexanone in toluene to form codeinone, with yield of codeinone reported to be less than 50%.
Ninan et al., Tetrahedron 48:6709-6716 (1992) describes the reaction of 3-O-dimethyl-t-butylsilylmorphine with manganese dioxide in chloroform at 25° C. to form 3-O-dimethyl-t-butylsilylmorphinone.
The Ninan et al. reference also describes the reaction of 3-O-dimethyl-t-butylsilylmorphine with tetrapropyl ammonium perruthenate and N-methylmorpholine-N-oxide in dichloromethane at an unspecified temperature to form 3-O-dimethyl-t-butylsilylmorphinone in about 86% yield.
U.S. Pat. No. 6,013,796 to Huang et al., describes the reaction of 3-O-acetylmorphine with a complex formed of dimethylsulfoxide (“DMSO”) and oxalyl chloride in the presence of base (the “Swern oxidation process”) at −78° C. to provide the corresponding 3-acetylmorphinone in 73% yield. U.S. Pat. No. 6,013,796 also describes reacting 3-O-benzylmorphine under similar conditions to provide 3-O-benzylmorphinone in 65% yield. However, the described process requires at least 2.5 molar equivalents of DMSO per mole of morphine and generates malodorous dimethylsulfide as a by-product.
Despite these described methods, there remains a need for improved methods for making 3-O-protected morphinones.
The Swern oxidation process described above has been the focus of considerable research, because it avoids the use of aggressive inorganic oxidants such as MnO2 and is generally useful for oxidizing primary and secondary alcohols to aldehydes and ketones, respectively. For example, De Luca et al., J. Org. Chem. 66:7907-7909 (2001) describes the reaction of primary or secondary alcohols with a complex formed of DMSO and trichorocyanuric acid (“TCCA”) in tetrahydrofuran (“THF”) at −30° C. in the presence of triethylamine to provide the corresponding aldehydes and ketones, respectively. However, malodorous dimethylsulfide is formed as a by-product of the reaction. Accordingly, much effort has been spent modifying the Swern oxidation process or developing more attractive alternatives.
The following paragraphs relate to known modifications and alternatives to the Swern oxidation processes.
Nishide et al., Tetrahedron. Lett. 43:5177-5179 (2002) describes a low-odor Swern oxidation process using dodecylmethylsulfoxide as the sulfoxide reactant.
Harris et al., J. Org. Chem. 63:2407-2409 (1998) describes a low-odor Swern oxidation process using polymer bound 6-(methylsulfinyl)hexanoic acid as the sulfoxide reactant, and the sulfoxide reactant can be regenerated by reaction of the sulfide by-product with NaIO4.
An alternative to the Swern reaction is described in Corey et al., J. Am. Chem. Soc. 94:7586-7587 (1972), where a primary or secondary alcohol is reacted with a complex formed of dimethylsulfide and N-chlorosuccinamide (“NCS”) or Cl2 at −25° C. in the presence of a base (the “Corey-Kim oxidation”) to form the corresponding aldehyde and ketone, respectively. However, the Corey reference discloses that reaction of 2-cyclohexenol forms chlorocyclohexene rather than 2-cyclohexenone. Additionally, the described process uses malodorous dimethylsulfide as a reagent.
Ohsugi et al., Tetrahedron 59:8393-8398 (1992) describes a low-odor Corey-Kim oxidation process where a primary or secondary alcohol is reacted with CH3S(C12H25) and NCS in the presence of triethylamine at −40° C., but the described process uses at least a 3-fold molar excess of the sulfide and NCS per mole of alcohol.
Despite these described methods, there remains a need for improved methods for oxidizing primary or secondary alcohols to the corresponding aldehydes or ketones, respectively.
Citation of any reference in Section 2 of this application is not an admission that the reference is prior art to the application.